Currently, an inverter is typically a switching power converter constituted by semiconductor components, mainly used for converting DC (direct current) power into AC (alternative current) power or pulsating DC power.
For an inverter based on conventional full-bridge topology, in a modulation mode using bipolar PWM (pulse width modulation), switching losses are huge, thus efficiency is low. In modulation using unipolar PWM, leakage currents are large, which affects safety of systems (i.e., the switching power converters). Therefore, based on the conventional full-bridge topology, neither of the two types of modulation meets the requirements in inverter production.
To solve the above problems, an inverter with six-transistor topology is proposed.
FIG. 1 is a schematic circuit diagram of a switching power converter with six-transistor topology of the prior art. As shown in FIG. 1, the topology includes: three bridge arms in parallel, in which a first bridge arm only includes a first filter capacitor C, a second bridge arm is constituted by switch transistors S3, S6 and S4 connected in series, and diodes D3, D6 and D4 are respectively connected in antiparallel with the switch transistors S3, S6 and S4. A third bridge arm is constituted by a switch transistor S1 and a switch transistor S2 connected in series, and diodes D1 and D2 are respectively connected in antiparallel with the switch transistors S1 and S2. A switch transistor S5 is connected the common node of the switch transistor S3 and the switch transistor S6 with the common node of the switch transistor S1 and the switch transistor S2. A diode D5 is connected in antiparallel with the switch transistor S5. A filtering circuit constituted by an inductor L1, a second filter capacitor Ch and an inductor L2. The two terminals of the second filter capacitor Ch connect to two terminals of AC side of the switching power converter respectively. One terminal of the inductor L1 connects with one terminal of the AC side, the other terminal of the inductor L1 connects with the common node of the switch transistor S1 and the switch transistor S2; one terminal of the inductor L2 connects with the other terminal of AC side, the other terminal of the inductor L2 connects with the common node of the switch transistor S6 and the switch transistor S4. At DC side of the switching power converter, there is the first filter capacitor C which connects between a positive terminal DC+ and a negative terminal DC−. The second filter capacitor Ch is a high-frequency filter capacitor. Herein each switch transistor and the diode connected in antiparallel therewith are collectively referred to as a power transistor unit. In addition, to make the description easy, it is assumed that an output voltage Vout or an output current Tout of the AC side Vac has a positive direction as indicated by arrows in FIG. 1, that is, the switching power converter serves as an inverter.
The switching power converter with six-transistor topology shown in FIG. 1 may solve the problems of the high switching losses in bipolar PWM modulation and the large leakage current in unipolar PWM modulation, moreover, the topology shown in FIG. 1 may also operate in a rectifier mode under certain circumstances. Since the switching power converter with six-transistor topology shown in FIG. 1 is a switch circuit, and constituted by semiconductor switch components such as MOSFETs (metal-oxide-layer semiconductor field effect transistors), IGBTs (insulated gate bipolar transistors) and diodes, in which the switch components operate at high frequencies in a switching mode (particularly when the switch components shown in FIG. 1 operate alternately), energy stored in parasitic inductance in commutation loops will be dissipated on the circuits during switching, and meanwhile, voltage spikes across the components will be increased due to the circuit parasitic parameters, which may reduce reliability of the system. That is to say, in the switching power converter, large circuit parasitic inductance may result in undesirable electrical characteristics of the switch circuit thereof. Therefore, a layout of the components in the switch circuit of the switching power converter needs to be optimized.
In addition, as users desire for electronic products with thin, small sizes and other properties, switching frequencies for the switch circuit of the switching power converter tend to be increased. Moreover, with the development of semiconductor components, new types of semiconductor components such as silicon carbide components and gallium nitride components emerge, which have even higher operating frequencies and lower conduction losses. Therefore, in the future, switching power converter products require the circuit parasitic inductance to be even smaller.